Centrifugal pumps often operate over a wide range of hydraulic operating or capacity conditions. This results in problems caused by radial thrust in single volute pumps.
When the pump is operating close to shut-off or very close to shut-off conditions, a high radial thrust is produced. This can be minimized by the use of double or twin volute casings or by a circular casing, but many times construction limitations prohibit the use of such casings.
Assuming these construction limitations apply and it is not possible to use a double or twin volute casing or a circular casing, and a single volute casing should best be used, the radial thrust loads on the impeller must be taken into account. These loads will cause a deflection of the impeller drive shaft and the impeller thereon, which can be calculated.
Where the deflection of the drive shaft does not result in stresses which exceed the fatigue limit of the shaft, a single volute pump is feasible and may be so designed as to accommodate the deflection which occurs from the large radial thrust loads on the pump. This can be done by forming the front and rear shrouds of the impeller on arcs struck from a common center at the bearings for the shaft or between the bearings for the shaft where the shaft requires at least two bearings, and particularly where the bearings may be ball or roller bearings. The interior walls of the pump housing are also formed along arcs struck from the same center to provide close running clearance between the front and rear shrouds, and the pumping chamber, to avoid the danger of damage that may occur by catastrophic contact between the impeller and any of the stationary surfaces of the pump housing.
A mechanical seal spaced outwardly of the inboard bearings should take the place of the conventional stuffing box. The sealing faces of the mechanical seal should be formed from arcs struck from the same center as the center of the arcs along the back and front shrouds of the impeller. This accommodates free oscillatable movement of the shaft about the center of the radius of curvature of the front and rear shrouds of the impeller and the sealing faces of the pumping chamber.
A principal advantage of the present invention over prior centrifugal pumps is that by forming the impeller and interior walls of the pump housing to accommodate radial movement of the impeller and cantilever drive shaft therefor, under high thrust conditions on the impeller, damage to the impeller and pump housing, which would normally be caused by radial excursions of the cantilever shaft, is avoided.
A further advantage of the invention is the provision of a high capacity volute cantilever shaft pump in which the impeller may move relative to the volute pump housing about an axis centered at the bearings for the cantilever drive shaft without the liability of damaging the impeller or pump housing.
A further advantage of the invention is in the replacement of the conventional stuffing box for the cantilever drive shaft for the impeller by a mechanical seal in which the sealing faces of the seal are concentric with the front and rear shrouds of the impeller, and form effective seals during radial movement of the drive shaft for the impeller, caused by high thrust conditions on the impeller.
A principal object of the invention, therefore, is to improve upon the high capacity cantilever pumps heretofore in use by mounting the impeller drive shaft to move radially about an axis between the outboard bearings for the shaft and to provide clearance between the pump housing and front and rear shrouds of the impeller which conforms to radial movement of the shaft under high load conditions.
A still further object of the invention is to improve upon the high capacity volute types of cantilever shaft driven pumps heretofore in use, by contouring the impeller to enable it to move radially about an axis, the center of which is at the center of the inboard bearings for the impeller shaft, and to conform the pump housing to radial movement of the impeller, to compensate for the high radial thrust conditions occurring during starting and shut-off conditions of the pump.
A still further object of the invention is to provide a new and improved lined cantilever pump in which the lining is a wear and corrosion resistant material and is formed to allow radial movement of the impeller relative to its housing when the pump is operating under low capacity conditions, such as may be encountered when the impeller is operating very close to shut-off conditions or at actual shut-off conditions.
A still further object of the invention is to improve upon the high capacity volute pumps heretofore in use by lining the interior of the pump chamber with a corrosion resistant material which conforms to radial movement of the impeller, caused by radial excursions of its cantilever drive shaft, when operating under conditions close to shut-off conditions or at actual shut-off conditions.
Other objects, features and advantages of the invention will readily be apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure.